This invention relates to compositions based on natural and/or synthetic elastomers containing olefinic double bonds that have acoustic damping properties in the vulcanized state.
Manufacturers of vehicles, machines, and appliances use very thin-walled panels in fabrication to reduce the weight and size of the manufactured articles. Mechanically moving parts or operating motors inevitably cause these thin-walled panels to vibrate. The vibrations are propagated in the form of solid-borne sound throughout the vehicle, machine, or appliance, and can be radiated into the air at remote locations. To reduce that sound radiation these panels are typically equipped with sound-damping linings.
Vehicle manufacturers use various technologies for the damping of vibrations in vehicle body structures in order to reduce noise in the passenger compartment of the vehicles. A conventional solution is the use of asphalt damping pads, comprising mixtures of bitumen and fillers, manually installed and thermally bonded to the sheet metal composing the vehicle body structures. This is difficult, time-consuming, and labor-intensive, and can introduce dirt and contaminants into the vehicle body paint shop resulting in paint finish defects; moreover, the asphalt sheets are brittle and tend to split away from the panel at low temperatures.
Currently, thick film coatings prepared from other polymer systems are being designed and used to replace melt-on asphalt damping pads. Although these are improvements on the asphalt damping pads, they are not problem free. Water-based acrylic, polyvinyl acetate, and ethylene/vinyl acetate emulsions, containing fillers, have been developed and can be sprayed onto the sheet-metal parts at the required lining thickness. However, they have the disadvantages that the water, at sufficiently thick coatings, cannot be removed rapidly enough to process industrial volumes efficiently, and the coatings can crack and shrink resulting in less consistent damping performance.
Thick-film coatings using solid plastisol compositions at nearly 100% solid polymers have been used in attempts to eliminate volatile content. However, plastisol sound damping compounds are not reliably cross-linking and they become soft and lose stiffness at elevated temperatures. This causes the sound damping performance to be lower.
Epoxy-based compositions usually consist of flexible epoxy resins and rigid epoxy resins. The cost of flexible epoxy resins tends to be high, and the cost of curing also tends to be high. The curing of an epoxy coating with a latent crosslinker requires a minimum of 160° C. at automotive production line speed.
In an effort to reduce the complexity of vehicles, machines, and appliances, and thereby decrease manufacturing costs, sprayable low viscosity liquid polybutadiene sound damping compositions containing a sulfur vulcanization agent have been attempted that allow robotic application at precise locations at room temperature or at only slightly elevated temperature. However, there is still a need for compositions that give improved sound damping while avoiding the drawbacks described above.